Spilling the Beans

John Spencer, Cassini Scientist on the Composite Infrared Spectrometer (bio)

Well, now it can be told!  It’s frustrating for me to sit on exciting
new results – when we’ve found something cool in our data I want to
tell everyone all about it right away.  But it’s important to present
mission results in a coherent and coordinated way, and of course we
have to take the time to be sure we have our facts straight.  So
we’ve waited till today, Wednesday 26th March, 2 weeks after the
close Enceladus flyby, to spill the beans.

The days after the Wednesday March 12th Enceladus flyby were a blur
of frenzied activity for me as I worked to find the goodies in the
tens of megabytes of data that Cassini’s Composite Infrared
Spectrometer (CIRS) instrument had gathered during the flyby.  My
first peek at the uncalibrated data the next day, on Thursday
afternoon, was already thrilling – the glow of the tiger stripes was
visible not just at the usual 9 – 16 micron wavelength range where
we’d seen them before, but at wavelengths as short as 7 microns.  
Shorter wavelengths mean hotter temperatures (in the same way that
white-hot is hotter than red-hot), so it looked like the fractures
might be warmer than we had thought.  By the time I got all the files
I needed for the full analysis, from CIRS’s home at the Goddard
Spaceflight Center, it was time for dinner.  Precious ones and zeros
that had been flying through the Saturn system onboard Cassini 24
hours earlier, and squirted overnight across the solar system at the
speed of light, made the final leg of their journey to analysis by
bicycle, as I cycled home with my laptop.

After dinner I got comfortable on the sofa and dived in.  By bedtime
I had a preliminary map of the heat radiation from the south pole, at
four times the resolution of our previous best map.  Each of the four
tiger stripe fractures, clearly resolved in the thermal infrared for
the first time, lit up with the bright glow of internal heat.  A
couple of other fractures, not previously suspected to be active,
were warm too.  By Friday afternoon I also had preliminary
temperature estimates for the fractures- yes, they were pretty warm,
at least 180 Kelvin!  That’s -135 Fahrenheit, which isn’t exactly
toasty until you consider that the surrounding terrain is at around
65 Kelvin or -342 Fahrenheit.  The highest temperatures we’d seen on
the previous flyby in July 2005 were much lower, around 145 Kelvin
(-198 Fahrenheit)- not because Enceladus’s fractures were cooler
then, but because the older, more distant, scans were less
sensitive.  If it’s 180 K on the surface it must be even warmer down
below, perhaps approaching the magic number of 273 Kelvin or +32
Fahrenheit, where Enceladus’ ubiquitous ice can melt to form the holy
grail of astrobiology, liquid water.

Since that initial frenzy I’ve been checking calibration and refining
details, preparing graphics for today’s press briefing, and hearing
by e-mail and telecons about all the great data that was gathered by
the rest of Cassini’s arsenal of science instruments during the
flyby, some of which will be revealed by Hunter Waite at today’s
telecon.  We’ve also been modifying plans for upcoming flybys based
on the new data- we now know the hottest and most interesting parts
of the south polar region and can zero in on them next time.  Already
the theoretically-inclined members of the Cassini science team are
honing their models of the south polar plumes based on the new
findings, and the rest of the planetary science community will soon
be following suit.  And this is just the beginning- there are seven
more Enceladus flybys to come in the next two years.

I’ll end this blog with a big thank you to the rest of the CIRS
team.  I’ve been doing the fun job of analyzing these data, but there
would be no CIRS data to analyze without the tireless efforts of the
many folks at Goddard Spaceflight Center who designed and built CIRS
back in the 1990s, keep it running, design the observations, and
calibrate the data.  Special thanks are due to my CIRS colleagues
John Pearl and Marcia Segura, and CIRS Principal Investigator Mike
Flasar.